In automotive applications, the motor vehicle includes one or more cooling fans and one or more heat exchangers (i.e., one each for the engine cooling system, the transmission, the air conditioning, and electrical components) which are mounted to the front of the motor vehicle, wherein the one or more fans provides a stream of forced air through the fins of the one or more heat exchangers.
As shown by way of example at FIG. 1, a fan assembly 10 includes two fans 12, 14, each having fixed pitch blades 16. The fans 12, 14 are typically driven mechanically by the engine, either by the crankshaft or by a belt-driven accessory pulley spinning at engine speed, wherein electro-viscous clutch mechanisms are commonly employed to selectively disable the fan (these clutch mechanisms can incur viscous friction and energy loss to heat), or alternatively each fan is powered electrically, wherein the electric motor rotational speed may be either preset or variable.
Under various driving conditions, more or less fan forced air flow is necessary. For example, a large amount of fan forced air is required, as for example on hot days when the motor vehicle is running but stopped or is traveling slowly, towing or traveling on an upgrade. On the other hand, little or no fan forced air is necessary on cold days when the motor vehicle is traveling at high speed. Most driving conditions are between these two extremes, wherein it would be desirable for the fan forced air to adjust to the driving conditions so as to always provide an optimal air flow with the least amount of energy consumption to drive the one or more fans.
Variable pitch blades are known for fixed wing aircraft propellers and helicopter rotors. However, these applications involve complex and necessarily robust mechanisms that are unsuitable for fans of the type presently being considered, where minimization or elimination in parasitic loss is an important consideration.
What remains needed in the art is a simple and lightweight mechanism for adjusting fan pitch, which is particularly suited to automotive application.